Underwater hydraulic control valves, such as used in controlling production or drilling equipment in underwater wells have been controlled in the past by a plurality of electrical or hydraulic control lines. However, as the number of underwater devices to be controlled has increased, the physical size, number and expense of the pilot or control lines required has increased as well as increasing the likelihood of damage to the underwater extending lines, such as shown in U.S. Pat. No. 3,460,614.
The present invention is directed to various improvements in a hydraulic control system for controlling a plurality of hydraulically actuated underwater devices through a single hydraulic line in a desired sequence by applying predetermined pressure levels through the single hydraulic control line.